LANDSLIDES AND LINEAR INFRASTRUCTURE IN WEST-CENTRAL BRITISH COLUMBIA Marten Geertsema BC Forest Service, Prince George, BC Canada [email protected] James W. Schwab BC Forest Service, Smithers, BC Canada Andrée Blais-Stevens Geological Survey of Canada, Ottawa

RÉSUMÉ

Les mouvements de terrain destructifs sont communs à l’ouest central de la Colombie-Britannique (C.-B.). Ces mouvements incluent des coulées et des glissements de débris, des coulées de terre et d’argiles, des chutes de blocs, des glissements et des avalanches rocheuses et des mouvements complexes impliquant la roche et le sol. Les pipelines, les lignes de transmission électrique, les routes et les chemins de fer ont tous été affectés par ces types de mouvements, perturbant le service aux communautés. Nous fournissons des exemples de mouvements destructifs, de leurs impacts, et des conditions climatiques liées aux glissements de terrain. Nous considérons également les aléas de glissements de terrain pour l'ouest central de la C.-B. sous certains scénarios du changement climatique.

ABSTRACT Destructive landslides are common in west central British Columbia (BC). Landslides include debris flows and slides, earth flows and flowslides, rock falls, slides, and avalanches, and complex landslides involving both rock and soil. Pipelines, hydro transmission lines, roads and railways have all been impacted by these landslides, disrupting service to communities. We provide examples of the destructive landslides, their impacts, and the climatic conditions associated with the failures. We also consider future landsliding potential for west central BC under climate change scenarios.

Figure 1. Landslides and linear infrastructure in west central BC. The landslides shown are described in the text and represent a small portion of actual landslides in the area.

In : J. Locat, D. Perret, D. Turmel, D. Demers et S. Leroueil, (2008). Comptes rendus de la 4e Conférence canadienne sur les géorisques: des causes à la gestion. Proceedings of the 4th Canadian Conference on Geohazards : From Causes to Management. Presse de l’Université Laval, Québec, 594 p.

M. Geertsema et al.

1. INTRODUCTION zones. At higher elevations, the Mountain-Hemlock, Engelmann Spruce-Subalpine Fir and Alpine Tundra zones West central British Columbia (BC) is a rugged, but sparsely occur ( Meidinger and Pojar 1991). populated portion of the province (Figure 1). Nevertheless the area hosts important transportation corridors, linking its 2.3 Bedrock geology communities and providing Canadian access to the Orient. Infrastructure includes roads, railways, hydro transmission On the coast, the bedrock lies within the Coast-Cascades lines, and hydrocarbon pipelines. The cities of Kitimat and Belt and belongs to the Coast Plutonic Complex. It is mainly Prince Rupert are important deep sea ports that are composed of Paleozoic to early Tertiary granitic rocks and expected to undergo substantial growth to meet the needs Proterozoic to Paleozoic high-grade metamorphic rocks. of growing Asian economies. Recently, major oil pipelines Towards the east, the bedrock is part of the Intermontane have been proposed, connecting the North American Belt, which consists of sedimentary and volcanic rocks of network to a Pacific tidewater port at Kitimat. Jurassic-Cretaceous age intruded by Cretaceous-early Tertiary felsitic to porphyritic plugs (Duffel and Souther The purpose of this paper is to provide examples of various 1964; Clague, 1984). types of destructive landslides that impact linear infrastructure in west central BC. The list is by no means 2.4 Surficial geology all-inclusive, and many more events have occurred that are not recorded here. We also consider the impact of The surficial geology of the area was mapped and described projected climate change on the incidence of future by Clague (1984). During the last glaciation, approximately landslides. 15 ka BP, the area was covered by the Cordilleran Ice Sheet. The types of sediments deposited were mainly cobbly to bouldery tills. During glaciation, the weight of the 2. SETTING ice sheet caused isostatic depression of the Earth’s crust. During deglaciation, (11-12ka BP), the crust slowly 2.1 Physiography rebounded, but at a much slower rate than the melting of the ice sheet. This caused coastal river valleys to be inundated The study area is located within the Coast, Hazelton and by marine waters. Glaciomarine sediments, mainly Skeena mountain ranges of northwestern British Columbia laminated silts and clays, were deposited as glaciers melted (Holland, 1976). These mountains are part of the northwest and retreated up the valleys. In areas where ice was at a trending geological zones within the Canadian Cordillera standstill for an extended period of time (e.g., Terrace), called the Coast-Cascades Belt and the Intermontane Belt. deltaic sands and gravels were deposited. The area consists of rugged mountains cut by deep valleys filled with glacial and post-glacial sediments. Most A dynamic interpretation of the kinematics of rock slides was mountains have rounded, dome-like tops from glacial not offered until 1932 (Heim, 1932, pp 126-136). Skermer’s overriding with relatively uniform elevations varying between translation noted “Since it is a question of finding the 1800-2400 m. Higher peaks, up to 2800 m, project as extreme limits of the imminent landslide, the energy line has nunataks (Holland, 1976; Clague, 1984). to be drawn down from the highest point of the probable slide mass” (p. 130) However, “ the inclination of the straight 2.2 Climate and vegetation line between the uppermost scarp edge and the tip of the tongue of the stationary rubble stream has long since been Topography strongly influences air temperature and considered a characteristic factor for landslides”( p. 129) precipitation in the area. Temperatures decrease with and ‘After several studies, I found the character of a rock increasing elevation and distance inland. For example, in avalanche could best be compared by using the angle of January, the mean coastal temperature at Prince Rupert (52 reach of the central stream line.” (p. 106). For the purposes masl), is about 1.8ºC. In comparison, roughly 350 km in- of comparison, we, too, have used this angle, termed “the land, in the Bulkley Valley at Smithers (515 masl), the mean travel angle” by Cruden and Varnes (1996, Figure 3-7) in temperature is about -10.5ºC. Moreover, mean July this paper. We remember that, in some cases, it is a temperatures vary between 14-17 ºC in the valleys and conservative estimate of the peak travel angle first decrease by several degrees in elevation (Clague, 1984). employed in 1911. The travel angle of the Frank Slide along profile 9 is 15.4°. The predominant flow of moisture–laden air travels towards the east from the Pacific Ocean. Mean annual precipitation values for coastal mountains exceed 2500 mm and can be 3. LANDSLIDE TYPES IMPACTING LINEAR greater than 3500 mm in some areas. There is a marked INFRASTRUCTURE decrease in precipitation towards the east. For example, in the Bulkley Valley, mean annual precipitation values range Numerous types of landslides are common in the varied between 400-500 mm (Clague, 1984). terrain of west central BC. We provide examples of a few of the landslides that have damaged linear infrastructure in the The main valleys of the study area lie within the Coastal region, but also make reference to a number of significant Western Hemlock and Sub-Boreal Spruce biogeoclimatic landslides that have not damaged infrastructure. Included Landslide and linear infrastructure in West-Central British Columbia

are large rock slides, some of which transformed into debris avalanches and/or flows, debris flows, debris slides, earth flows in glacial lake sediments and in fine textured colluvium, and flowslides in sensitive glaciomarine sediments. The locations of the described landslides are shown in Figure 1.

The landslides damage infrastructure in two main ways. (1) Most commonly infrastructure is in the landslide runout zone and is struck by moving debris. (2) Occasionally infrastructure is placed on unstable ground and is moved suddenly or episodically as the main body (Cruden and Varnes 1996) of the landslide moves. Where rock slides, debris flows, and debris slides described here resulted in damage to infrastructure, it was always the result of the first case, where objects were struck by moving material. In contrast, earth flows and flowslides damaged infrastructure by carrying it along during movement.

Landslides also can have varying causes and triggers. Examples of causes can be inherent weakness in material, valley deepening, glacial debuttressing, road construction, excavation etc. Triggers can be rainfall, snowmelt, site loading, seismic activity, etc. Shallow landslides such as debris slides and flows are often triggered by intense rainfall. Deep seated landslides such as large rock slides, earth flows and flowslides tend to have longer hydrological response times (Egginton 2005).

3.1 Rock slides Figure 2. Large, long runout rock slides in west central BC. Six large rock slides have occurred in west central BC since See Figure 1 for locations. (A) The 1999 Howson rock slide 1978, five of which occurred since 1999, and four since entrained till and colluvium, severing a natural gas pipeline 2002. Three of the six rock slides severed a natural gas (1). Note the hydro transmission line (2) and the landslide pipeline. All of the rock slides had relatively long runouts. dammed lake (3). (B) The 2002 Zymoetz rock slide transformed into a channelized debris flow, dammed the The 1999 Howson rock slide (Figure 2a) occurred at 03:00 Zymoetz River, flooded an important Forest Service Road hours PDT on 11 September. The rock slide travelled 2.7 for more than a year, and ruptured a pipeline. The landslide km, entraining till and colluvium. It ruptured the natural gas traveled 4 km. (C) The 2002 Harold Price rock slide pipeline, and formed a lake. The initial rockslide involved 0.9 transformed into a debris avalanche and then into a M m3 and the entrained volume is estimated to be 1.5 M m3 channelized debris flow, traveling more than 4 km. (D) the (Schwab et al 2003). The initial movement involved toppling 2002 Verney rock slide on the outer coast traveled 630 m. and cliff collapse onto a glacier. The debris travelled over (E) The 2005 Sutherland rock slide transformed into a the glacier and entered a gully where it entrained soil and debris avalanche and traveled 1.6 km. transformed into a debris flow.

On 8 June, 2002, a rock slide involving 1.6 M m3 Two other large rock slides occurred in west central BC in transformed into a debris flow, damming the Zymoetz River, 2002, along with others elsewhere in the province and severing a natural gas pipeline (Figure 2b; Schwab et (Geertsema et al. 2006a). The Harold Price and Verney al. 2003; Boultbee et al. 2006). The landslide travelled 4.3 landslides occurred near Smithers and southeast of Prince km. An estimated 0.5 M m3 of debris, including blocks up to Rupert on the outer coast, respectively (Figure 1). The 7 m in diameter, dammed the river, causing flooding 1.5 km Harold Price landslide (Figure 2c) initiated in what upstream. Although the dam was overtopped almost appeared to be a rock glacier in a cirque basin sometime immediately, it is still an obstruction to river flow. Access to between 22 and 24 June. Interstitial ice was found in the a 3000 km2 basin was blocked for more than one year due main scarp. After travelling 1.3 km the rock slide to the flooding of a major Forest Service road. transformed into a debris avalanche entraining till and colluvium. 2.2 km from the source the debris avalanche became channelized into a debris flow. The total travel distance of the landslide was 4 km. The volume is estimated to be 1.6 M m3. The Verney landslide (Figure 2d) is less precisely dated (Geertsema et al. 2006a). It probably initiated as a rockfall. The landslide travelled 630 m over a M. Geertsema et al.

vertical range of 370 m, and entrained sandy, bouldery till derived from granodiorite.

On July 13, 2005 a complex rock slide - debris avalanche occurred near Sutherland River, 40 km west of Fort St. James, British Columbia (Figure 2e). The landslide impact was powerful enough to leave a seismic signal at the Fort St James seismic station. The rapid landslide traveled 1.6 km and involved 3M m3 of volcanic rock and soil. The landslide bifurcated in the runout zone. Pre-slide deformation was evident on aerial photographs and the slide site had been heavily impacted by mountain pine beetle.

3.2 Debris flows and floods

Debris flows and floods are common destructive landslides in west central BC. They typically initiate in steep source areas, travel through gullies, and deposit on fans in the Figure 3. A debris flow at Legate Creek lodged this large valley bottoms. Debris flows intergrade to debris floods boulder between two trees. (hyperconcentrated flows) and floods, with decreasing sediment concentrations. Many fans in west central BC are the product of all three processes (Wilford et al. 2003). All three processes can destroy infrastructure.

An example of a fan that is traversed by a major highway and subject to episodic debris flows (Figure 3) is near Legate Creek (Figure 1). Two debris flows closed the highway at separate times in July and August 2004 with volumes of 7,000 and 20,000 m3, respectively. On 28 May, 2007 a much larger debris flow crossed the highway, killing two people. An earlier debris flow in 1978 was also larger (Septer and Schwab 1995). Scars on trees record the 1978 event as well as an episode about 85 years ago.

Large fans at Hunter Creek, Gosnell Creek, and west of Telkwa routinely wash out roads during flood periods. Debris and water floods are more common on these large fans than debris flows, but linear infrastructure placed on these landforms still requires careful hydrogeomorphological Figure 4. Recent shallow debris avalanche severed a gas assessment. pipeline and a road near Prince Rupert. Photo Tom Bond.

Combinations of debris flows, slides, and avalanches have occurred in clusters during intense coastal rainstorms.

3.3 Debris slides and avalanches

Shallow, rapid debris slides and avalanches occur throughout west central BC, but are particularly common on the coast in shallow soils draping steep bedrock (Figures 4 and 5). These landslides typically initiate during intense rainstorms, after certain antecedent conditions are met. The landslides have closed roads and severed hydro transmission lines repeatedly at Porcher Island and Port Simpson. In October 2002, an intense storm triggered more than 12 debris slides that took out the power to Port Simpson. Similar landslides removed power poles on Porcher Island in 1998, 2001, and 2005.

Figure 5. A debris avalanche across Highway 16, near Prince Rupert. Photo Tom Bond.

Landslide and linear infrastructure in West-Central British Columbia

3.4 Earth flows A large landslide, referred to informally as the Bulbous Toe, Earth flows occur in a variety of materials ranging from till in the Telkwa River valley (Figure 6b) underwent rapid and lake sediment to colluvium. Rapid, low gradient earth movement in prehistoric time (BC Forest Service, flows can intergrade to the clay flowslides of Hungr et al unpublished data). In the historic period a portion of the (2001), and tend to occur only in advance phase lake landslide continues to advance as a slow-moving earth flow. sediments, buried by till (Geertsema et al. 2006a). The A major transmission line traverses the landslide, and slower moving earth flows in west central BC can occur in adjustments are periodically required for one of the towers. all of these materials. About 30 cm/year of movement over the past 10 years has occurred along the tower. The colluvium is derived from A series of large, rapid, low gradient earth flows near tuffaceous volcaniclastic rock. Other locations within the Houston involve areas of up to 100 ha. A 40 ha flow along Telkwa valley and within the volcanic rocks of the Telkwa Houston Tommy Creek, that occurred in the 1960’s involves formation are also experiencing landslide movement and more than 1.5 M m3 of material (Figure 6a). sagging slopes (Schwab and Kirk 2003).

Slow moving earth flows reactivated along the Morice River road following road upgrades in the 1970’s and a major wild 3.5 Flowslides fire in 1983. Millions of dollars were spent stabilizing the slopes and repairing a 15 km section of the road. The Large flowslides involving sensitive glaciomarine sediments failures occurred in till and glaciolacustrine sediment. have destroyed a railway, a highway, and a pipeline in the western portion of the study area (Figure 1). They tend to move along nearly horizontal gradients, up to slopes of 3º.

Septer and Schwab (1995) give a brief account of a flowslide south of Terrace that occurred during railbridge construction across Alwyn Creek. The landslide occurred at Mile 6.6 on the Canadian National railway line between Terrace and Kitimat and was reported in the Terrace Standard on 24 June 1953. The landslide buried bulldozers and other construction equipment, and resulted in the construction of an s-shaped trestle.

Two separate flowslides at Lakelse Lake ruptured the highway between Terrace and Kitimat in May and June 1962 (Clague 1978; Geertsema and Schwab 1997). Both landslides debouched into Lakelse Lake, carrying vehicles and equipment with them. Loading from a spoil berm associated with highway construction was the likely trigger in both cases. The landslides were not retrogressive, since they were triggered, where the highway crossed them, near the mid points of the zones of depletion. They involved about 11 and 15 M m3, respectively and traveled extremely rapidly (Ministry of Transportation, unpublished data).

In November 2003, a large flowslide on Khyex River ruptured a natural gas pipeline, disrupting service to Prince Rupert for approximately 10 days (Schwab et al. 2004a, 2004b). The landslide involved 4.7 M m3 of material and was 1.6 km long from crown to tip. The river was dammed over a distance of 1.7 km, and water was backed up for 10 km. Service was disrupted to Prince Rupert for ten days.

4. FUTURE HAZARD REGIMES

Landslides in mountainous terrain are strongly influenced by Figure 6. Earth flows in west central BC. (A) A rapid earth climatic factors, including precipitation and temperature flow (1) at Houston Tommy Creek involved advance phase (Evans & Clague, 1994). Catastrophic landslides at high glaciolacustrine sediments. (B) An advancing lobe (1) of the elevations may be especially responsive to increases in Bulbous Toe near Telkwa involves fine textured colluvium. temperature. Researchers have suggested that recent Note the leaning trees. This slow moving earth flow is melting of glaciers in BC has debuttressed rock slopes traversed by a hydro transmission line. One of the towers adjacent to glaciers, causing deep-seated slope deformation requires periodic adjustment. M. Geertsema et al.

and catastrophic failure (Holm et al., 2003) such as at 5. CONCLUSIONS Howson Glacier (Figure 2a). Linear infrastructure is at continued risk from a variety of Alpine permafrost may be degrading under the present landslide types in west central BC. The landslides range warmer climate, decreasing the stability of slopes (Harris et from shallow debris slides and flows, to massive rapid, rock al., 2001). Recent large rock avalanches in the European slides, and rapid low gradient earth flows and flowslides. Alps have been attributed to the melting of mountain The risk is likely to rise under scenarios of a warmer and permafrost, and this phenomenon may also play a role in wetter climate as the pressure for more infrastructure initiating landslides in northern British Columbia, as in the increases. More research is required to assess future case of the Harold Price landslide (Figure 2c). hazards. Remote sensing techniques could be employed to assess slope deformation that often precedes catastrophic The Mink Creek flowslide near Terrace occurred after nearly failure. Detailed slope deformation and runout models a decade of increasing temperature and precipitation. should continue to be developed to predict slope behaviour, Geertsema and Schwab (1997) provide evidence for an and to better delineate hazard and risk zones in valleys and increase in flowsliding 2000 to 3000 years ago in the corridors. Terrace area under wetter climatic conditions. Almost all global circulation models predict warmer and wetter conditions in the future for the Terrace area (Figure 6), thus 6. ACKNOWLEDGMENTS more such landslides may be expected in this area. We thank Gord Hunter, Frank Maximchuk, Matt Sakals, and Large scale climate changes also have implications for Jonathan Fannin for helpful reviews. forest insects and pathogens. More than 80% of the mature lodgepole pine in BC is expected to succumb to the mountain pine beetle within the next decade (Eng et al. 7. REFERENCES 2004). These changes to the forest are expected to have have widespread hydrological impacts to the landscape, and Boultbee, N., D. Stead, J.W. Schwab & M. Geertsema may predispose slopes to accelerated landsliding. (2006), The Zymoetz River rock avalanche, June 2002, British Columbia, Canada. Engineering Geology 83, pp. 76- 93.

Annual climate change scenarios for Terrace, British Columbia 25 Clague, J.J. (1978), Terrain hazards in the Skeena and Kitimat River basins, British Columbia. Geological Survey of Canada Paper 78-1A, pp. 183-188. 20 Clague, J.J. (1984), Quaternary geology and

15 geomorphology, Smithers-Terrace-Prince Rupert area, British Columbia. Geological Survey of Canada Memoir 413, 71 pp. 10

2020 Cruden D.M. & D.J. Varnes (1996), Landslide types and 5 2050 processes. In: Special Report 247: Landslides investigation Precipitation (%) and mitigation. A.K. Turner and R.L. Schuster (Eds.). 2080 0 National Research Council, Transportation Research Board, Washington D.C., pp. 36-75.

-5 Duffel, S. & J.G. Souther (1964), Geology of the Terrace map-area, British Columbia (103 I E 1/2). Geological

-10 Survey of Canada, Memoir 329. -101234567 Temperature (ºC) Egginton, V.N. (2005), Historical climate variability from the instrumental record in northern British Columbia and its Figure 6. Annual climate change scenarios for 2020, 2050, influence on slope stability. M.Sc. thesis. Simon Fraser and 2080 for Terrace, BC, with respect to a 1961-1990 University, Burnaby, British Columbia. 130 pp. global climate model baseline. The points represent the results of 58 different global circulation models, generally Eng, M., A. Fall, J. Hughes, T. Shore, B. Riel, P. Hall & A. predicting a progressively warmer and wetter climate for Walton (2005), Provincial level projection of the current Terrace. The data was obtained from the Canadian Institute mountain pine beetle outbreak: an overview of the model for Climate Studies web site (http://www.cics.uvic.ca), and is (BCMPB v2) and results of Year 2 of the project. Ministry of modified from Geertsema et al. (2006b). Forests Report, 51 pp.

Evans, S.G. & J.J. Clague (1994), Recent climatic change

and catastrophic geomorphic processes in mountain

environments. Geomorphology 10, pp. 107-128.

Landslide and linear infrastructure in West-Central British Columbia

Geertsema, M., J.J. Clague, J.W. Schwab & S.G. Evans Septer, D. & J.W. Schwab (1995), Rainstorm and flood (2006 a), An overview of recent large catastrophic damage: Northwest British Columbia 1891-1991. B.C. landslides in northern British Columbia, Canada. Ministry of Forests, B.C. Land Management Report 31, 196 Engineering Geology 83, pp.120-143. pp. Wilford, D.J., M.E. Sakals & J.L. Innes (2003), Forestry on Geertsema, M., D.M. Cruden & J.W. Schwab (2006 b), A fans; a problem analysis. Forestry Chronicle 79, pp. 291- large rapid landslide in sensitive glaciomarine sediments at 296 Mink Creek, northwestern, British Columbia, Canada. Engineering Geology 83, pp. 36-63.

Geertsema, M. & J.W. Schwab (1997), Retrogressive flowslides in the Terrace-Kitimat, British Columbia area: From early post-deglaciation to present - and implications for future slides. Proceedings, 11th Vancouver Geotechnical Society Symposium, Vancouver, BC, pp. 115-133. Geertsema, M & Torrance, J.K. (2005), Quick clay from the Mink Creek landslide near Terrace, British Columbia : Geotechnical properties, mineralogy, and geochemistry. Canadian Geotechnical Journal 42, pp. 907-918. Harris, C., M.C.R. Davies & B. Etzelmüller (2001), The assessment of potential geotechnical hazards associated with mountain permafrost in a warming global climate. Permafrost and Periglacial Processes 12, pp. 145-156. Holland S.S. (1976) Landforms of British Columbia. British Columbia Department of Mines and Petroleum Resources, Bulletin 48, 138 p. Holm, K., M.J. Bovis, & M. Jakob (2004), The landslide response of alpine basins to post-Little Ice Age glacial thinning and retreat in southwestern British Columbia. Geomorphology 57, pp. 201-216. Hungr, O. & S.G. Evans (2004), Entrainment of debris in rock avalanches; an analysis of a long run-out mechanism. Bulletin, Geological Society of America 116, pp. 1240–1252. Hungr O., S.G. Evans, M. Bovis, & J.N. Hutchinson (2001) Review of the classification of landslides of the flow type. Environmental and Engineering Geoscience, 7:221-238. Meidinger, D.V. & J.J. Pojar (1991), Ecosystems of British Columbia. B.C. Ministry of Forests Special Report Series, no. 6, 330 pp.

Schwab, J.W., A. Blais-Stevens & M. Geertsema (2004), The Khyex River flowslide, a recent landslide near Prince Rupert, British Columbia. 57th Canadian Geotechnical Conference, Quebec City, Canada. 1C, pp. 14-21. Schwab, J.W., M. Geertsema & A. Blais-Stevens (2004), The Khyex River landslide of November 28, 2003, Prince Rupert British Columbia, Canada. Landslides 1, pp. 243- 246. Schwab, J.W., M. Geertsema & S.G. Evans (2003), Catastrophic rock avalanches, west-central B.C., Canada. 3rd Canadian Conference on Geotechnique and Natural Hazards, Edmonton, AB, pp. 252-259.

Schwab, J.W. & M. Kirk (2003), Sackungen on a forested slope, Kitnayakwa River. British Columbia Ministry of Forests, Prince Rupert Forest Region. Extension Note 47, 6 pp. M. Geertsema et al.